sorry i give board exam with rbse board not cbse

and how to give improment exam please mujhe detail me btaye

Hello,

Are you asking about CBSE boards in yoyr question, because I guess there is a typing error there. Anyways, coming to the point, tje eligibility criteria for taking admission in NITs and IITs is to have a minimum aggregate of 75 percentage in your class 12th CBSE Boards or to be in top 20 percentile of your respective state boards. Since you have scored less than 75 percentage in CBSE Boards, I would suggest you to look for options available at this percentage or if you want a seat in NIT or IIT, you should take CBSE Improvement exam next year along with taking JEE.